Device for protecting electrical contacts against unauthorized access



Invento y A cv'; /7025 Altomey H. HOLT DEVICE FOR PROTECTING ELECTRICAL CONTACTS AGAINST UNAUTHORIZED ACCESS Flled May 26, 1945 Aug. 1, 1950 Patented Aug. 1, 1950 DEVICE FOR PROTECTING ELECTRICAL CONTACTS AGAINST UNAUTHORIZED ACCESS Harry Holt, Denton, near Manchester, England, assignor to Oldham & Son Limited, Denton, near Manchester, England, a, British company Application May 26, 1 945, Serial No. 595,966

In Great Britain June 21, 1944 1 Claim.

This invention relates to a device for protecting electrical contacts against unauthorized access.

The invention is particularly applicable to accumulator hand lamps for use in mines or places in which an explosive atmosphere may exist, of the type in which electrical contacts are provided for connection of the accumulator to a charging means. When the lamp is in use, it is desirable that access to the contacts be prevented to avoid the risk of a spark. Devices have been employed in which the contacts are protected by a cover which can be opened to give access to the contacts only by breaking a seal. Such devices, however, do not prevent access, and their normal use entails trouble in first breaking the seal and, after charging, resealing the cover.

The object of the invention is a device for locking the cover of the contacts which prevents the cover being unlocked by unauthorized persons, enables it to be easily unlocked, locks the cover automatically and is not liable to be damaged by rough usage and occupies very little space.

According to the invention, a member is normally in the path of the cover Of the contacts and preventing its motion to give access to the contacts and an iron armature is connected with the member, the member and armature being adapted to be moved against yielding pressure to an unlocking position in which the member is out of the path of the cover; a casing encloses the armature and member against access, the casing being located close to the armature when the armature is in the unlocking position, whereby the member can be moved from the locking to the unlocking position on actuating the armature by applying a magnet to the outside of the casing. The cover is a sliding shutter, the mem her being normally in the plane in which it slides, and, when the shutter has been moved to give access to the contacts, being prevented from returning to its normal position by abutment against the shutter until, on the return movement of the shutter, it returns under the yielding pressure to its normal locking position.

In order that the invention may be more clearly understood, an embodiment thereof will now be be described, by way of example, by reference to the accompanying drawing showing a vertical section through a part of the casing of an accumulator lamp and wherein like reference numerals designate the same or similar parts.

The casing of the accumulator lamp is shown at I, and 2, 2 are the contact sockets connected to the terminals of the accumulator. Access to the contacts 2, 2 is normally prevented by a cover in the form of a shutter 3, adapted to slide into the position shown in dotted lines, to give access to the contacts. An iron armature 4 is pivoted to a support-on the casing at 5 and has a lug 6 adapted to pass through a hole 1 in the casing. In its normal position, shown in full lines, the lug 6 is through the hole l and obstructs the passage of the shutter 3 to its position giving access to the contacts. A spring 8 tends to keep the armature 4 in its normal position. The armature 4 is enclosed within a casing 9 fixed to the casing I. The casing 9 is preferably of non-magnetic material and is as close as is practicable to the outer surface of the armature 4, when the lug 6 is withdrawn from the position in which it obstructs the movement of the shutter 3 to a position (shown in dotted lines) in which it permits the shutter to be moved.

In operation, when access to the contacts 2 is to be obtained for charging, a permanent or electromagnet is applied to the casing 9, as indicated by the permanent magnet I 0, shown in dotted lines, to withdraw the armature 4 and lug 6 to the position shown in dotted lines, and the shutter 3 is then moved to expose the contacts 2. On removing the magnet, the lug 6 abuts against the surface of the shutter. After charging, the shutter 3 is moved back to cover the contacts, and the armature 4 and lug 6 then automatically return to the position in which the lug locks the shutter against opening.

The casing 9 may be of steel provided that it is thin enough not appreciably to shield the armature from the magnet.

The lug 6 is shown integral with the armature 4, but it may be an independent member, and may be pivoted, and then the armature 4 is attached to it, or connected with it, so that the movement of the armature when attracted by a magnet withdraws the lug 6.

By pivoting the armature close to the case of the accumulator lamp and locating it in a position approximately parallel to the case, the projection of the device from the case is reduced to small limits' The advantages of the device are that the cover of the contacts is unlocked by the momentary application of a magnet; that re-locking is automatic; that the cover cannot be unlocked by anyone not in possession of a suitable and strong enough magnet; that all moving parts are pro tested against damage from rough usage; that the device can be applied to the outside of an accumulator lamp casing of customary form by aperturing the casing I and then applying over the aperture a casing, such as 9, enclosing an armature 4; The casingso appliedincreasesxthe,

outside dimensions of'this casing by only a small amount which, in practice, need not exceed onequarter to five-sixteenths of an inch.

The casing may be in the form of a box, that is comprising a cover 9 and a base plate. (notishown) between which is totally enclosed the armature such as 4, the base plate being apertured to register with the peI1iilg"T=i! 1theCaS='- ing I for the projection of thelug'fi oithearmature.

I claim:

An accumulator lamp comprising incombinae tion a lamp case, contact sockets secured inter? nally of said case to receive the terminals of an accumulator, an aperture in said case to provide access tosaidsockets, a shutter for said aperture mounted for slidingmovement in the case to aperture'closing and exposing positions, an' iron' armature'pivotall y mounted on the outside of said case to pivot'about an axis approximately parallel'with and close to the case, yielding means-to urge the armature towards the case,

a latch movableiwith the armature to project through an opening in the case, said latch being normally in the plane in which the shutter slides and retaining the shutter in aperture closing position, and an armature casing secured to the outside of the lamp case and enclosing the armature and latch, the armature casing being located close to the armature when the armature is in delatching position whereby the latch can be moved from the latching to the delatching position. on actuating the armature by applying a magnet to the'outside of the armature casing, the latch being retainable in detached position by 'the shutter when the latter is moved to aperture exposing'position.

HARRY HOLT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number: Name I Date 455,126 Smith et a1 June 30,1891 767,298. Louis .Aug.- 9,- 1904 1,743,540 Gosmannet a1 Jan. 14, 1930 1,779,780 Pilla Oct. 28, 1930 1,905,774 Wheat Apr. 25,1933 

